Conventionally, a bending machine such as a press brake (FIG. 25(A)) comprises a punch P mounted on an upper table 52 and a die D mounted on a lower table 53, and moves either one of the tables upward or downward to bend a work W by cooperation of the punch P and die D.
In this case, before the bending operation, the work W is positioned at a predetermined position by being butted on a butting face 50 which is set behind the lower table 53.
In a case where an automatic bending operation is carried out with the use of a robot, the work W is positioned by a gripper 51 of the robot supporting the work W to place the work W on the die D and butt the work W on the butting face 50.
In order to bend a work W having its C portion forming-processed as shown in FIG. 25(B), one end A of the work W is supported by the gripper 51 of the robot, and the other end B is butted on the butting face 50.
However, in this case, the portion of the work W between the other end B and the portion placed on the die D is mildly curved as shown in FIG. 25(A).
Accordingly, the butting of the work W against the butting face 50 by the gripper 51 of the robot becomes very unstable, making it impossible to achieve accurate positioning. If a human worker determines the position of the work W by holding the work W, accurate positioning might be available due to the worker's sense developed over years. However, a robot can not achieve accurate positioning by trial and error.
Further, in a case where a corner of a work W is to be bent along a bending line m as shown in FIG. 26(A), positioning of the work W can not be carried out by butting the work W on the butting face 50. Furthermore, in a case where the bending line m and a work end surface T are not parallel with each other as shown in FIG. 26(B), the positioning accuracy might be lowered even if the work W is butted on the butting face 50. The intended bending operation can not be performed in either case.
An object of the present invention is to position a work accurately by carrying out electronic positioning by using image processing, even in a case where mechanical positioning by using a butting face is impossible.